Toshimasa Tanaka

Structural Analysis of the Mechanism of Inhibition and Allosteric Activation of the Kinase Domain of HER2 Protein.

Aberrant signaling of ErbB family members human epidermal growth factor 2 (HER2) and epidermal growth factor receptor (EGFR) is implicated in many human cancers, and HER2 expression is predictive of human disease recurrence and prognosis. Small molecule kinase inhibitors of EGFR and of both HER2 and EGFR have received approval for the treatment of cancer. We present the first high resolution crystal structure of the kinase domain of HER2 in complex with a selective inhibitor to understand protein activation, inhibition, and function at the molecular level. HER2 kinase domain crystallizes as a dimer and suggests evidence for an allosteric mechanism of activation comparable with previously reported activation mechanisms for EGFR and HER4. A unique Gly-rich region in HER2 following the α-helix C is responsible for increased conformational flexibility within the active site and could explain the low intrinsic catalytic activity previously reported for HER2. In addition, we solved the crystal structure of the kinase domain of EGFR in complex with a HER2/EGFR dual inhibitor (TAK-285). Comparison with previously reported inactive and active EGFR kinase domain structures gave insight into the mechanism of HER2 and EGFR inhibition and may help guide the design and development of new cancer drugs with improved potency and selectivity.

2-{3-[4-(Alkylsulfinyl)phenyl]-1-benzofuran-5-yl}-5-methyl-1,3,4-oxadiazole derivatives as novel inhibitors of glycogen synthase kinase-3beta with good brain permeability.

Glycogen synthase kinase 3beta (GSK-3beta) inhibition is expected to be a promising therapeutic approach for treating Alzheimers disease. Previously we reported a series of 1,3,4-oxadiazole derivatives as potent and highly selective GSK-3beta inhibitors, however, the representative compounds 1a,b showed poor pharmacokinetic profiles. Efforts were made to address this issue by reducing molecular weight and lipophilicity, leading to the identification of oxadiazole derivatives containing a sulfinyl group, (S)-9b and (S)-9c. These compounds exhibited not only highly selective and potent inhibitory activity against GSK-3beta but also showed good pharmacokinetic profiles including favorable BBB penetration. In addition, (S)-9b and (S)-9c given orally to mice significantly inhibited cold water stress-induced tau hyperphosphorylation in mouse brain.

Identification of Benzoxazin-3-one Derivatives as Novel, Potent, and Selective Nonsteroidal Mineralocorticoid Receptor Antagonists

Mineralocorticoid receptor (MR) blockade has come into focus as a promising approach for the treatment of cardiovascular diseases such as hypertension and congestive heart failure. In order to identify a novel class of nonsteroidal MR antagonists that exhibit significant potency and good selectivity over other steroidal hormone receptors, we designed a novel series of benzoxazin-3-one derivatives and synthesized them from 6-(7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-6-yl)-2H-1,4-benzoxazin-3(4H)-one (1a), high-throughput screening (HTS) hit compound. Our design was based on a crystal structure of an MR/compound complex and a docking model. In the course of lead generation from 1a, a 1,2-diaryl framework was characterized as a key structure with high binding affinity. On the basis of scaffold hopping and optimization studies, benzoxazin-3-one derivatives possessing 1-phenyl-3-trifluoromethylpyrazol-5-yl moiety at the 6-position were identified as a novel series of potent and selective MR antagonists. Among these compounds, 6-[1-(4-fluoro-2-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-5-yl]-2H-1,4-benzoxazin-3(4H)-one (14n) showed highly potent activity and good selectivity and also exhibited a significant antihypertensive effect in deoxycorticosterone acetate-salt hypertensive rats. On the basis of these results, compound 14n was progressed for further pharmacological evaluation.

Regioselective Friedel–Crafts acylation of 1,2,3,4-tetrahydroquinoline and related nitrogen heterocycles: effects of NH protective groups and ring size

Regioselectivity of the Friedel–Crafts acylation of the following nitrogen heterocycles was studied: 2,3-dihydro-1H-indoles 3, 1,2,3,4-tetrahydroquinolines 4, 2,3,4,5-tetrahydro-1H-1-benzazepines 5 and 1,2,3,4,5,6-hexahydro-1 -benzazocines 6. It was found that though the ratio of regioisomers depends on ring size, it can be controlled by changing the NH protective groups. A molecular orbital (MO) calculation of the Lewis acid co-ordinated substrates gave a rational explanation of the regioselectivity.

Design and Synthesis of Pyrrolo[3,2-d]pyrimidine Human Epidermal Growth Factor Receptor 2 (HER2)/Epidermal Growth Factor Receptor (EGFR) Dual Inhibitors: Exploration of Novel Back-Pocket Binders

To develop novel human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) kinase inhibitors, we explored pyrrolo[3,2-d]pyrimidine derivatives bearing bicyclic fused rings designed to fit the back pocket of the HER2/EGFR proteins. Among them, the 1,2-benzisothiazole (42m) ring was selected as a suitable back pocket binder because of its potent HER2/EGFR binding and cell growth inhibitory (GI) activities and pseudoirreversibility (PI) profile as well as good bioavailability (BA). Ultimately, we arrived at our preclinical candidate 51m by optimization of the N-5 side chain to improve CYP inhibition and metabolic stability profiles without a loss of potency (HER2/EGFR inhibitory activity, IC(50), 0.98/2.5 nM; and GI activity BT-474 cells, GI(50), 2.0 nM). Reflecting the strong in vitro activities, 51m exhibited potent tumor regressive efficacy against both HER2- and EGFR-overexpressing tumor (4-1ST and CAL27) xenograft models in mice at oral doses of 50 mg/kg and 100 mg/kg.

Discovery of Imidazo[1,5-c]imidazol-3-ones : Weakly Basic, Orally Active Factor Xa Inhibitors

The coagulation enzyme factor Xa (FXa) has been recognized as a promising target for the development of new antithrombotic agents. We previously found compound 1 to be an orally bioavailable FXa inhibitor in fasted monkeys; however, 1 showed poor bioavailability in rats and fed monkeys. To work out the pharmacokinetic problems, we focused our synthetic efforts on the chemical conversion of the 4-(imidazo[1,2- a]pyridin-5-yl)piperazine moiety of 1 to imidazolylpiperidine derivatives (fused and nonfused), which resulted in the discovery of the weakly basic imidazo[1,5- c]imidazol-3-one 3q as a potent and selective FXa inhibitor. Compound 3q showed favorable oral bioavailability in rats and monkeys under both fasted and fed conditions and antithrombotic efficacy in a rat model of venous thrombosis after oral administration, without a significant increase in bleeding time (unlike warfarin). On the basis of these promising properties, compound 3q was selected for further evaluation.

Regioselective Friedel–Crafts acylation of 2,3,4,5-tetrahydro-1H-2-benzazepine and related nitrogen heterocycles

It is revealed that NH-protected 2,3,4,5-tetrahydro-1H-2-benzazepine 4 is acylated on C-8 with greater than 95% regioselectivity. This regioselectivity has been applied to the synthesis of 3-(1-benzylpiperidin-4-yl)-1-(2,3,4,5-tetrahydro-1H-2-benzazepin-8-yl)propan-1-one 3a, an inhibitor of acetylcholinesterase (AChE). The regioselectivities of the acylation of the following nitrogen heterocycles have also been studied: 4-formyl-2,3,4,5-tetrahydro-1,4-benzoxazepine 6, 2,3,4,5-tetrahydro-1H-2-benzazepin-3-one 7, 2,3,4,5-tetrahydro-1H-3-benzazepin-2-one 8, 7,11b,12,13-tetrahydro-5H-isoindolo[2,1-b][2]benzazepin-7-one 9 and 6,7,9,13b-tetrahydro-5H-isoindolo[1,2-a][2]benzazepin-9-one 10. A molecular orbital (MO) calculation on the Lewis acid coordinated substrates has been used for predicting regioselectivity.

Selective coupling reactions of alkynyl(phenyl)iodonium tosylates with alkynylcopper reagents

Alkynyl(phenyl)iodonium tosylates react with mixed cuprates coordinated by alkynyl components to give unsymmetrical diacetylenes selectively; the coupling reaction with dialkylcuprates afforded substituted alkynes.